VIEWING THE RENAL EPITHELIUM WITH THE ATOMIC-FORCE MICROSCOPE

The atomic force microscope (AFM) was invented in 1986. It created the possibility to study the surfaces of biological material at the molec ular level. The AFM is not only a microscope with atomic resolution (a t least when applied to suitable samples) but is also an instrument wi th a broad variety of other applications. We present five examples dem onstating the application of the AFM technique in different ways, main ly in renal epithelium. First, it was used as a high-resolution near-f ield microscope which generated images of canine kidney chromosomes. S econd, dynamic changes of the plasma membrane of canine kidney cells w ere visualized with a resolution at least 10-fold greater than that ob tainable by light microscopy. Third, the AFM was used as a tool which interacted directly with the plasma membrane of canine kidney cells. F ourth: due to its excellent resolution in the third dimension (namely height), continuous measurements of changes in 'height' of multimers o f cloned plasma membrane potassium channel proteins of rat kidney (ROM K1) in response to ATP were performed with a time resolution of about 100 ms in physiological buffer. Fifth, the AFM continuously followed d issociation processes of multimeric macromolecules (such as transcript ion factors) under physiological conditions and: on the basis of indiv idual molecular volume measurements, allowed estimation of the number of monomers in a multimeric complex. Taken together, the AFM offers a wide spectrum of novel approaches for the experimental nephrologist.